Disclosed herein is a method for checking, without contact, whether a torque which is required to open a plastic screw closure which is screwed onto a bottle corresponds to a predetermined value. Also disclosed is an apparatus for carrying out this method.
Plastic screw closures for bottles are known from German Patent Document Nos. 24 39 414 A and 20 2007 009 983 U1. The lead of the single-start screw thread of a plastic screw closure lies at 2-3 mm. In a capping machine, plastic screw closures are screwed onto the bottles passing through by a concurrent capping head in each case clasping and tightening a closure which is loosely disposed on the bottle mouth.
When a plastic screw closure is screwed onto a bottle, the torque applied during the tightening is set according to empirical values. If this torque is set too weak then there is a risk of the bottle becoming untight. If the torque is set too high, on the other hand, the users require aids to open the plastic screw closure, which is likewise undesired.
According to the state of the art, the torque necessary for opening a plastic screw closure is checked manually by the bottles being opened manually using a torque measuring device and the measurement values being recorded. This method can also be automated by automatically diverting a bottle at certain time intervals and then determining the torque which is necessary in order to loosen the closure slightly and then close it again.
A method is known from German Patent Document No. 10 2008 062 385 by which it can be established in the case of plastic containers whether a tamper-evident closure has already been damaged during the closing of the cap. In addition, the tamper-evident closures are illuminated at an angle from below and examined from the opposite side by an opto-electronic sensor system. The torque for opening the closure is thus not checked.
A method is known from European Patent Document No. 1 293 473 in which the correct positioning of the closure on the bottle is checked. In addition, various parameters are determined, among others the height of the bottle and the upright alignment of the closure. Also in this method the torque required for opening the closure is not checked.
A method is known from European Patent Document No. 2 439 488 by which the rotational position of the thread portion is established in the case of a blank for the blow moulding of a plastic bottle. The rotational position is, for example, determined from the distance between the mouth edge and the thread turn or from a comparison of the opening section with a plurality of saved models. Also in this method the torque required for opening the closure is not checked.
It is known from European Patent Document No. 0 572 758 to bring the label and the closure of a bottle into a predetermined orientation to each other. In addition, the orientation of each bottle is determined mechanically or optically by marks on the bottle and the closure is applied according to the orientation of the bottle. The bottle and the closure are thereby located in a predetermined relative rotational position.